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Revenue (Details) - CAD ($) $ in Millions |  | 12 Months Ended
--- | --- | ---
Oct. 01, 2019 | Dec. 31, 2020 | Dec. 31, 2019
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | $ 2 | $ 0
Canadian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 13 |
Australian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 2,594 |
Alberta Thermal |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 336 |
Hydro |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 31 |
Wind and Solar |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 13 |
Later than one year | Hydro |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 8 |
Second to fifth years inclusive | Australian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | $ 203 |
Genesee 3 |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Ownership percentage sold |  |  | 50.00%
Minimum |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Contracts for sale of byproducts of coal combustion, term |  | 1 year |
Minimum | Canadian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | $ 4 |
Minimum | Australian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | 100 |
Minimum | Wind and Solar |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | 2 |
Minimum | More than five years |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 2 |
Minimum | 2023 | Alberta Thermal |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 5 |
Minimum | Annually thereafter | Alberta Thermal |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | $ 40 |
Maximum |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Contracts for sale of byproducts of coal combustion, term |  | 3 years |
Maximum | Canadian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | $ 5 |
Maximum | Australian Gas |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | 126 |
Maximum | Wind and Solar |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Performance obligations satisfied |  | 5 |
Maximum | More than five years |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 3 |
Maximum | 2023 | Alberta Thermal |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | 10 |
Maximum | Annually thereafter | Alberta Thermal |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Transaction price allocated to remaining performance obligations |  | $ 45 |
Keephills 3 |  |  |
Disclosure of disaggregation of revenue from contracts with customers [line items] |  |  |
Proportion of ownership interest in joint operation | 50.00% |  | 50.00%

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